1 //===----------------------------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8
9 #ifndef _LIBCPP___ALGORITHM_SHIFT_RIGHT_H
10 #define _LIBCPP___ALGORITHM_SHIFT_RIGHT_H
11
12 #include <__algorithm/move.h>
13 #include <__algorithm/move_backward.h>
14 #include <__algorithm/swap_ranges.h>
15 #include <__config>
16 #include <__iterator/iterator_traits.h>
17 #include <__utility/swap.h>
18 #include <type_traits>
19
20 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
21 # pragma GCC system_header
22 #endif
23
24 _LIBCPP_BEGIN_NAMESPACE_STD
25
26 #if _LIBCPP_STD_VER > 17
27
28 template <class _ForwardIterator>
29 inline _LIBCPP_INLINE_VISIBILITY constexpr
30 _ForwardIterator
shift_right(_ForwardIterator __first,_ForwardIterator __last,typename iterator_traits<_ForwardIterator>::difference_type __n)31 shift_right(_ForwardIterator __first, _ForwardIterator __last,
32 typename iterator_traits<_ForwardIterator>::difference_type __n)
33 {
34 if (__n == 0) {
35 return __first;
36 }
37
38 if constexpr (__is_cpp17_random_access_iterator<_ForwardIterator>::value) {
39 decltype(__n) __d = __last - __first;
40 if (__n >= __d) {
41 return __last;
42 }
43 _ForwardIterator __m = __first + (__d - __n);
44 return _VSTD::move_backward(__first, __m, __last);
45 } else if constexpr (__is_cpp17_bidirectional_iterator<_ForwardIterator>::value) {
46 _ForwardIterator __m = __last;
47 for (; __n > 0; --__n) {
48 if (__m == __first) {
49 return __last;
50 }
51 --__m;
52 }
53 return _VSTD::move_backward(__first, __m, __last);
54 } else {
55 _ForwardIterator __ret = __first;
56 for (; __n > 0; --__n) {
57 if (__ret == __last) {
58 return __last;
59 }
60 ++__ret;
61 }
62
63 // We have an __n-element scratch space from __first to __ret.
64 // Slide an __n-element window [__trail, __lead) from left to right.
65 // We're essentially doing swap_ranges(__first, __ret, __trail, __lead)
66 // over and over; but once __lead reaches __last we needn't bother
67 // to save the values of elements [__trail, __last).
68
69 auto __trail = __first;
70 auto __lead = __ret;
71 while (__trail != __ret) {
72 if (__lead == __last) {
73 _VSTD::move(__first, __trail, __ret);
74 return __ret;
75 }
76 ++__trail;
77 ++__lead;
78 }
79
80 _ForwardIterator __mid = __first;
81 while (true) {
82 if (__lead == __last) {
83 __trail = _VSTD::move(__mid, __ret, __trail);
84 _VSTD::move(__first, __mid, __trail);
85 return __ret;
86 }
87 swap(*__mid, *__trail);
88 ++__mid;
89 ++__trail;
90 ++__lead;
91 if (__mid == __ret) {
92 __mid = __first;
93 }
94 }
95 }
96 }
97
98 #endif // _LIBCPP_STD_VER > 17
99
100 _LIBCPP_END_NAMESPACE_STD
101
102 #endif // _LIBCPP___ALGORITHM_SHIFT_RIGHT_H
103